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BRITISH PHARMACEUTICAL CONFERENCE. 
will rectify the mistake. If the manipulation has been correctly performed, it 
will be indicated by the colour. The dark-brown colour instantly disappears on 
boiling, the precipitate obtaining the bright-green of chromic oxide, whilst the 
solution becomes a bright yellow. 
The chromic oxide is washed, but for accurate results the hydrated chromic 
oxide retains the chloride of potassium too tenaciously to ignite and weigh 
directly. It is better to redissolve the washed hydrated chromic oxide in 
diluted hydrochloric acid, and to reprecipitate with ammonia in the usual 
manner. This gives the most exact results ; but there are quicker methods. 
Thus, the hydrated chromic oxide might be washed and converted into chromic 
acid by Chancel’s method (by peroxide of lead), and estimated volumctrically. 
Chromic Oxide found x 1 -354 = Nitrite of Sodium 
4Cr 2 0 3 +3N 2 0 3 = 3N 2 0 5 +2Cr 4 0 3 . 
The second process is based upon the first, that both nitrites and nitrates of 
the alkalies are converted into chloride upon ignition with chloride of ammo¬ 
nium. Pure nitrite of sodium gives 84-78 per cent, of chloride of sodium, whilst 
nitrate of sodium only gives 68-82. From these data, it is therefore easy to 
calculate the percentage, as anything under 84-78 indicates the presence of 
nitrate. 
It must be borne in mind, that if the specimen contains carbonate, this would 
give the percentage of nitrite too high. As 100 parts of carbonate would 
give 110-37 parts of chloride of sodium after ignition, therefore it will be neces¬ 
sary to deduct an equivalent quantity of chloride of sodium from the results 
before calculating them. A weighed quantity of the nitrite is intimately mixed 
with powdered chloride of ammonium, and introduced into a platinum crucible, 
a gentle heat is applied, until the whole of the excess of sal ammoniac and 
other gaseous bodies are volatilized. The residue is dissolved in water, and the 
chloride of sodium estimated volumetrically with a silver solution. 
After a deduction for any carbonate of sodium present, the calculation may 
be made thus:— 
(Na Cl — 68-82) -f 100 , 
15-96 ’ 
x being the percentage of nitrite of sodium. The chloride of sodium left, 
minus the percentage of nitrate, divided by the difference (15-96), will give the 
percentage of nitrite, or vice versa :— 
(84-78 — Na Cl) + 100 
15-96 
x being in this case nitrate of sodium. 
Nitrate of ammonium in solution is resolved on boiling into nitrogen and 
water. The applicability of this phenomenon to the estimation of nitrites will 
form the subject of a future communication. 
Many of the numerous experiments necessarily performed in connection with 
this paper were made by my late assistant, Mr. Arthur Cranwill, to whom I 
take this opportunity of tendering my thanks. 
NOTE ON NITItITE OF SODA. 
BY MR. W. D. HOWARD. 
Mr. Warington’s able paper in the ‘Pharmaceutical Journal’ for July, has 
pretty much exhausted this subject. I do not, however, remember to have 
seen noticed a tolerably ready method for purifying the rough nitrite of soda 
from much of the undecomposed nitrate which in practice it always retains. 
This method consists in taking advantage of the slight difference in solubility 
